1. Field of the Invention
The present invention relates generally to fiber optic splice connectors, and more particularly, to a splice connector having a stub optical fiber and means for verifying an acceptable splice termination between a field optical fiber and the stub optical fiber.
2. Technical Background
Optical fibers are useful in a wide variety of applications, including the telecommunications industry in which optical fibers are employed for voice, data and video transmission. Due, at least in part, to the extremely wide bandwidth and the low noise operation provided by optical fibers, the variety of applications in which optical fibers are being used is continuing to increase. For example, optical fibers no longer serve merely as a medium for long distance signal transmission, but are being increasingly routed directly to the home or business, and in some instances, directly to a desk or other work location. With the ever increasing and varied use of optical fibers, apparatus and methods have been developed for coupling optical fibers to one another outside the controlled environment of a factory setting, commonly referred to as “field installation” or “in the field.” For example, field installations are typically performed in a telephone central office, in an office building, and in various types of outside plant terminals. However, in order to efficiently couple the optical signals transmitted along the fibers, a fiber optic connector must not significantly attenuate, reflect or otherwise alter the optical signals. In addition, fiber optic connectors for coupling optical fibers must be relatively rugged and adapted to be connected and disconnected a number of times in order to accommodate changes in the optical transmission path that may occur over time.
Although fiber optic connectors can generally be most efficiently and reliably mounted upon the end portion of an optical fiber in a factory setting during the production of a fiber optic cable assembly, many fiber optic connectors must be mounted upon the end portion of an optical fiber in the field in order to minimize cable lengths and to optimize cable management and routing. As such, a number of fiber optic connectors have been developed specifically to facilitate field installation. One advantageous type of fiber optic connector designed specifically to facilitate field installation is the UNICAM® family of field-installable fiber optic connectors available from Corning Cable Systems LLC of Hickory, N.C. Although the UNICAM® family of field-installable connectors share a number of common features, including a common termination technique (i.e., mechanical splice), the UNICAM® family also offers several different styles of connectors, including mechanical splice connectors adapted to be mounted upon a single optical fiber and mechanical splice connectors adapted to be mounted upon two or more optical fibers. Regardless, each field-installable fiber optic connector requires a method of determining whether the continuity of the optical coupling between the fiber optic connector and a field optical fiber mounted to the fiber optic connector is acceptable. As used herein, this process is generally referred to as “verifying an acceptable splice termination.” Typically, a splice termination is acceptable when a characteristic related to the optical performance of the connector, such as insertion loss or reflectance, is within a prescribed limit or threshold value.
A conventional field-installable fiber optic connector 10 is illustrated in FIGS. 1A and 1B. By way of example, the fiber optic connector 10 shown and described is a field-installable LC style UNICAM® mechanical splice connector developed by Corning Cable Systems LLC for interconnecting an optical fiber cable in the field to an optical connector, optical component or optical device. However, the concepts described herein are generally applicable to verifying the continuity of the optical coupling between any pair of interconnected optical fibers, and more particularly, between a field optical fiber and a stub optical fiber of any fiber optic splice connector, including a single fiber or multifiber fusion splice or mechanical splice connector. Examples of typical single fiber mechanical splice connectors are provided in U.S. Pat. Nos. 4,755,018; 4,923,274; 5,040,867; and 5,394,496. Examples of typical multifiber mechanical splice connectors are provided in U.S. Pat. Nos. 6,173,097; 6,379,054; 6,439,780; and 6,816,661. As shown herein, the mechanical splice connector 10 includes a ferrule 12 defining a lengthwise, longitudinal bore for receiving a stub optical fiber 14. The stub optical fiber 14 is preferably sized such that one end extends outwardly beyond the rear end 13 of the ferrule 12. The mechanical splice connector 10 also includes a pair of opposed splice components 17, 18, at least one of which defines a lengthwise, longitudinal groove for receiving and aligning the end portion of the stub optical fiber 14 and an end portion of a field optical fiber 15 of an optical cable upon which the connector 10 is to be mounted. As shown herein, the lower splice component 18 comprises a single lengthwise extending groove 19 for receiving and aligning the stub optical fiber 14 and the field optical fiber 15.
As shown, the mechanical splice connector 10 further includes a ferrule holder 16 for receiving the ferrule 12 and the splice components 17, 18. A cam member 20 is disposed about a medial portion of the ferrule holder 16 for engaging at least one of the splice components 17, 18, and to thereby secure the end portions of the stub optical fiber 14 and the field optical fiber 15 between the splice components, as will be described. In certain embodiments, the ferrule holder 16 has a view port 21 formed partially therethrough and located medially between the opposed ends of the ferrule holder for a purpose to be described hereinafter with reference to one of the preferred embodiments of the invention. A conventional lead-in 22 may be provided to guide the end portion of the field optical fiber 15 and an exposed length of a protective coating or buffer 25 into the rear of the ferrule holder 16. Furthermore, an optional crimp tube 24 may be disposed within the rear end of the lead-in 22 and employed to strain relieve the coating or buffer 25 of the fiber to the lead-in a known manner. The forward end of the ferrule holder 16 is disposed within a connector housing 26 and biased forwardly by a coil spring 28 retained inside the connector housing between the ferrule holder and a spring retainer 30. The outer jacket 35 of the optical cable and/or any strength elements 36 provided between the outer jacket and the buffer 25 may be positioned over the rear end of the ferrule holder 16 so that a conventional crimp band 32 may be employed in a known manner to strain relieve the optical cable to the connector 10. Finally, a flexible boot 34 may be positioned over the optical cable to prevent the optical cable from exceeding the minimum bend radius of the field optical fiber 15 immediately adjacent the rear of the connector 10. An optional trigger 38 having a flexible finger push 39 may be positioned over the cam member 20 with the finger push opposite a flexible latch 27 depending from the connector housing 26. If provided, the finger push 39 may be depressed to assist in moving the latch 27 to insert and remove the mechanical splice connector 10 from, for example, a dense optical patch panel. The fiber optic mechanical splice connector 10 is described in greater detail in co-pending U.S. patent application Ser. No. 10/808,057 filed on Mar. 24, 2004, and assigned to the assignee of the present invention.
In order to mount the mechanical splice connector 10 upon the field optical fiber 15, the splice components 17, 18 are positioned proximate the rear end 13 of the ferrule 12 with the end portion of the stub optical fiber 14 extending rearwardly from the ferrule disposed within the groove 19 defined by the splice components. Once the connector 10 is assembled as shown in FIG. 1B, the end portion of the field optical fiber 15 can be inserted into the rear end of the connector 10 and guided by the lead-in 22 and optional crimp tube 24 into the groove 19 defined by the splice components 17, 18. By advancing the field optical fiber 15 into the groove 19 defined by the splice components 17, 18, the end portion of the field optical fiber eventually makes physical contact with the end portion and the stub optical fiber 14 and establishes an optical connection, or coupling, between the stub optical fiber and the field optical fiber. The termination of the field optical fiber 15 to the fiber optic connector 10 is completed by actuating the cam member 20 to bias the splice components 17, 18 together, and thereby secure the end portions of the stub optical fiber 14 and the field optical fiber 15 within the groove 19 defined by the splice components. In the exemplary embodiments provided herein, the cam member 20 is actuated (also referred to “cammed” or “closed”) by rotating the cam member about the ferrule holder 16 and relative to the splice components 17, 18. If the continuity of the optical coupling between the stub optical fiber 14 and the field optical fiber 15 is acceptable (e.g., the insertion loss is less than a prescribed value and/or the reflectance is greater than a prescribed value), the cable assembly can be completed. The cable assembly may be completed, for example, by crimping the rear end of the crimp tube 24 onto the buffer 25 and/or crimping the crimp band 32 onto the jacket 35 and/or strength members 36 positioned over the rear end of the ferrule holder 16. Finally, the flexible boot 34 previously positioned over the optical cable may be slid forward over the rear of the connector 10 and secured thereto using an adhesive, heat-shrink or other suitable means.
Installation tools have also been developed to facilitate the splice termination of an optical fiber to a fiber optic splice connector, and particularly, to terminate a field optical fiber to a mechanical splice connector. Examples of typical installation tools for facilitating the connectorization of one or more optical fibers to a mechanical splice connector in the field are described in U.S. Pat. Nos. 5,040,867; 5,261,020; 6,816,661; and 6,931,193. In particular, U.S. Pat. Nos. 6,816,661 and 6,931,193 describe a UNICAM® installation tool available from Corning Cable Systems LLC of Hickory, N.C. designed specifically to facilitate mounting the UNICAM® family of fiber optic connectors upon the end portions of one or more field optical fibers. In general, the installation tool supports the mechanical splice connector 10 (including the ferrule 12 and the splice components 17, 18) while the field optical fiber 15 is inserted into the connector and aligned with the stub optical fiber 14. In this regard, the installation tool includes a tool base, a tool housing positioned on the tool base, and an adapter provided on the tool housing. The adapter has a first end for engaging the mechanical splice connector 10 to be mounted upon the field optical fiber 15, and an opposed second end that serves as a temporary dust cap. The forward end of the mechanical splice connector 10 is received within the first end of the adapter, which in turn is mounted on the tool housing. The end portion of the field optical fiber 15 is then inserted into the open rear end of the mechanical splice connector 10 and the splice components 17, 18 are subsequently biased together, for example by engagement of the cam member 20 with a keel portion provided on at least one of the splice components, in order to secure the stub optical fiber 14 and the field optical fiber 15 between the splice components. In the particular example of the installation tool shown and described in U.S. Pat. Nos. 6,816,661 and 6,931,193, the cam member 20 is actuated by rotating a cam actuator arm provided on the tool housing about ninety degrees (90°) around the longitudinal axis of the mechanical splice connector 10 from a generally vertical position to a generally horizontal position. As the cam member 20 rotates, the radially inner surface of the generally cylindrical cam member engages the keel portion of the lower splice component 18 extending through a slot provided on the ferrule holder 16 to urge the lower splice component to move in the direction of the upper splice component 17.
Once the fiber optic connector 10 is mounted upon the end portion of the field optical fiber 15 (i.e., the field optical fiber is terminated to the connector), the resulting fiber optic cable assembly is typically tested end-to-end. Among other things, testing is conducted to determine whether the optical continuity established between the stub optical fiber 14 and the field optical fiber 15 is acceptable. While optical connections and fiber optic cables can be tested in many different manners, a widely accepted test involves the introduction of light having a predetermined intensity and/or wavelength into the stub optical fiber 14 or the field optical fiber 15. By measuring the light propagation through the fiber optic connector 10, and more particularly, by measuring the insertion loss and/or reflectance using an optical power meter or Optical Time Domain Reflectometer (OTDR), the continuity of the optical coupling between the stub optical fiber 14 and the field optical fiber 15 can be determined. If testing indicates that the optical fibers are not sufficiently coupled (for example the end portion of the field optical fiber 15 and the end portion of the stub optical fiber 14 are not in physical contact or are not aligned) the operator must either scrap the entire fiber optic cable assembly or, more commonly, replace the fiber optic connector 10 in an attempt to establish the desired optical continuity. In order to replace the fiber optic connector 10, the operator typically removes (i.e., cuts) the mechanical splice connector off of the field optical fiber 15 and discards the connector. The operator then repeats the splice termination process described above utilizing a new mechanical splice connector disposed on the installation tool and mounting the new mechanical splice connector onto a re-cleaved end portion of the field optical fiber. Field-installable mechanical splice connectors are known that permit the splice termination to be reversed, and thereby avoid the need to scrap the entire fiber optic cable assembly or the fiber optic connector. Regardless, significant time and expense is still required to mount the fiber optic connector onto the field optical fiber, remove the cable assembly from the installation tool, conduct the continuity test and, in the event of an unacceptable splice termination, repeat the entire process.
In order to facilitate relatively simple, rapid and inexpensive continuity testing, Corning Cable Systems LLC of Hickory, N.C. has developed installation tools for field-installable mechanical splice connectors that permit continuity testing while the connector remains disposed on the installation tool. As previously described, the installation tool includes an adapter having opposed first and second ends, the first end of which is adapted to receive the mechanical splice connector 10. In order to test the continuity of the optical coupling between the stub optical fiber 14 and the field optical fiber 15, an optical power generator, such as a laser diode, is provided to deliver a visible wavelength (e.g., red) laser light to the area within the splice connector 10 where the end portion of the stub optical fiber meets the end portion of the field optical fiber, referred to herein as the “splice joint,” or alternatively, the “termination area.” In a particular embodiment, the visible light is delivered through the stub optical fiber 14 to the termination area via a test optical fiber mounted upon a mating test connector received within the second end of the adapter. Alternatively, a laser diode may be positioned immediately adjacent the end face 11 of the ferrule 12 opposite the stub optical fiber 14. As a result, the termination area is illuminated with visible light that produces a “glow” indicative of the amount of light from the stub optical fiber 14 being coupled into the field optical fiber 15. At least a portion of the connector 10 is formed of a non-opaque, optically transmissive (e.g., translucent or transparent) material, for example the splice components 17, 18, the ferrule holder 16, and/or the cam member 20, so that the glow emanating from the termination area is visible to an operator.
By monitoring the dissipation of the glow emanating from the termination area (i.e., from the stub optical fiber 14) before the end portion of the field optical fiber 15 is in physical contact with the end portion of the stub optical fiber and after the field optical fiber is terminated to the fiber optic connector 10, the operator can determine whether there is sufficient physical contact and/or alignment between the field optical fiber 15 and the stub optical fiber. In particular, continuity of the optical coupling between the stub optical fiber 14 and the field optical fiber 15 is presumed to be established if the amount of glow visible before the end portion of the field optical fiber 15 is in physical contact with the end portion of the stub optical fiber 14 dissipates below a threshold amount when the field optical fiber is terminated to the connector 10. Once the end portion of the field optical fiber 15 is in physical contact with the end portion of the stub optical fiber 14, the cam member 20 of the fiber optic connector 10 can be actuated to fix the position of the field optical fiber 15 relative to the stub optical fiber 14 within the splice components 17, 18, and to thereby terminate the field optical fiber to the connector. In instances when the splice termination is unacceptable (i.e., the initial glow emanating from the termination area does not dissipate below the threshold amount), the field optical fiber 15 may be repositioned relative to the stub optical fiber 14 and again terminated to the fiber optic connector 10 until the splice termination is acceptable. As previously mentioned, the installation tool may permit the cam member 20 to be un-actuated (i.e., reversed) in the event that the splice termination is unacceptable, thereby releasing the splice components 17, 18, so that the field optical fiber 15 can be repositioned relative to the stub optical fiber 14 and again terminated to the fiber optic connector 10.
The Corning Cable Systems LLC method for verifying an acceptable splice termination described above is commonly referred to as the “Continuity Test System” (CTS) and the combined functionality of the visible light laser, test optical fiber and test connector are commonly referred to as a “Visual Fault Locator” (VFL). In practice, the method is generally sufficient for determining whether the majority of splice terminations are acceptable since the quality of the splice need not be maintained to a high degree of precision and the operator is typically highly-trained and experienced. However, in certain circumstances, for example when a fiber optic network requires an exceptionally low insertion loss, it is important to maintain the quality of the splice termination to a greater degree of precision. At the same time, it is desirable to utilize less highly-trained and experienced operators in order to reduce the overall cost of installing a fiber optic network. In such situations, a potential shortcoming of the above-described CTS method using a VFL is the variability of the amount of glow emanating from the termination area before the field optical fiber 15 is positioned in physical contact with the stub optical fiber 14 and after the field optical fiber is terminated to the mechanical splice connector 10. In particular, it may be difficult even for a highly-trained and experienced operator to assess whether the change in the amount of glow emanating from the termination area before and after the field optical fiber 15 is terminated to the fiber optic connector 10 is substantial enough to indicate an acceptable splice termination. Variations in the ambient light, variations in the translucence of different fiber optic connectors, the operating condition of the VFL and the adapter, the subjectivity of the operator, and the variability introduced by different operators conducting the same test for different splice terminations are just some of the factors that contribute to the varying and inconsistent results that may be obtained when conducting continuity testing using a VFL.
Furthermore, depending upon the translucence of the fiber optic connector and the intensity of the visible laser light, the termination area may continue to glow appreciably (sometimes termed “nuisance glow”) even after an acceptable splice termination. As a result, a less highly-trained or less experienced operator may attempt multiple insertions of the field optical fiber or repeated splice terminations using the same fiber optic connector in an effort to further diminish or entirely eliminate the nuisance glow in an acceptable splice termination. These misguided efforts of the untrained or inexperienced operator typically cause damage to the fiber optic connector or to the field optical fiber, or in the least, result in optical performance less than that which would have been achieved had the operator accepted the first termination, even though the glow was not completely diminished and the nuisance glow persisted. Contrary to the common understanding within the industry, it is the properly scaled difference in the amount of glow emanating from the termination area before and after the field optical fiber 15 is terminated rather than the residual amount of glow that is most critical in determining whether a particular splice termination is acceptable. Accordingly, improved apparatus and methods are needed to reduce the overall time and cost required to verify an acceptable splice termination. In particular, improved apparatus and methods are needed to reduce the subjectivity presently introduced by an operator when verifying an acceptable splice termination in a field-installable fiber optic connector, and to thereby correspondingly increase the efficiency and accuracy of determining whether a particular splice termination is acceptable. Preferably, such apparatus and methods should accommodate existing installation tools for field-installable fiber optic connectors, and more preferably, accommodate existing installation tools for single fiber and multifiber field-installable mechanical splice connectors.
Additional features and advantages of the invention are set forth in the detailed description which follows and will be readily apparent to those skilled in the art from that description, or will be readily recognized by practicing the invention as taught by the detailed description, the drawings and the appended claims. It is to be understood that both the foregoing general description and the following detailed description present exemplary embodiments of the invention as well as certain preferred embodiments. As such, the detailed description is intended to provide an overview or framework for understanding the nature and character of the invention as recited in the appended claims. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated into and constitute a part of this specification. The drawings illustrate various preferred embodiments of the invention, and together with the detailed description, serve to explain the principles and operations thereof. However, the drawings and descriptions are intended to be merely illustrative, and therefore, should not be construed so as to limit the scope of the claims in any manner.